This invention relates to an optoelectronic mounting structure that may be used in conjunction with an optical transmitter, receiver or transceiver module.
Fiber optics are one of the most important new media for transmitting information. Fiber optics are capable of carrying enormous quantities of voice, data and video traffic on light impulses over hair-thin glass fibers. Fiber optics transmit more information and data over a shorter period of time than circuit-transmission media. For example, optical signals may be transmitted over fiber optics with losses of less than 0.1 dB/km. In sharp contrast, data generally is transmitted over a pair of twisted copper wires with losses of up to 50 dB/km. The capabilities of fiber optics have fundamentally changed communications.
The fiber optics industry has exploded as the Internet and telecommunication field have created a skyrocketing demand for broadband, high-speed pipe lines to carry data. Long-span fiber optic networks of 100 kilometers or more carry bandwidth ranging from 40 to 50 giga bites per second. Similarly, high-speed fiber optics are capable of connecting wide-area networks of approximately 200 kilometers. Also, fiber optics may connect metropolitan networks of 500 meters to 2 kilometers, such as connecting one building to another building. The largest growth area for high-speed fiber optics, however, is connecting distances of less than 300 meters. In this sub-300 meter or short-distance market, fiber optics are used for a wide variety of purposes, including connecting computers within a room and linking routers, switches and transport equipment.
While significant progress has been made in the area of fiber optics, more wide-spread use is dependent upon the availability of a low cost, easy-to-use and efficient (i.e., low loss of light) optical transmitter and receiver module to link fiber optics to various electronic devices and components such as computers and routers. A critical aspect of such a module is the accurate alignment and attachment of the individual optical fibers to the electronic devices that transmit and receive light streams to and from the optical fibers. These electronic devices, known as optoelectronic devices, use optical and electronic technology or optoelectronics to convert electrical signals into optical radiation or light and transmit the radiation into optical fibers. Other optoelectronic devices receive optical radiation from optical fibers and convert it into electrical signals for processing. Accurate alignment and attachment of the individual optical fibers to the optoelectronic devices is essential to achieving a good and efficient optical connection, one that produces a low loss of light at the interface between the optical fibers and the optoelectronic devices.
A known method for precisely coupling optical fibers to optoelectronic devices is active alignment. Specifically, a photo-detector is placed at one end of an optical fiber, and an optoelectronic device, such as a vertical cavity surface emitting laser, is placed near the other end of the optical fiber. After turning on the laser, the optical fiber is manipulated manually around the light-emitting surface of the laser until the photo-detector detects the maximum amount of optical radiation as indicated by an output electrical signal. Similarly, a photo-detector can be actively coupled to an optical fiber by transmitting laser light into one end of an optical fiber and manually adjusting the position of the other end of the optical fiber relative to the photo-detector until the detector receives the maximum amount of optical radiation.
Actively aligning an array of optical fibers to an array of optoelectronic devices is not practical because the dimensions of an optoelectronic device and the cross-section of an optical fiber are small and multiple dimensions of rotation and translation motion must be controlled. The active alignment process to connect even a single optical fiber strand to an optoelectronic device is usually time-consuming and requires knowledge, skill and expertise. The active alignment process is particularly laborious and time-intensive when a number of optical fibers must be individually aligned to an array of optoelectronic devices. This process requires a variety of relatively complex and costly components that significantly increase the fabrication costs to produce precisely aligned optical devices. Moreover, during the active alignment process, optoelectronic devices emit a significant amount of optical power and energy. The heat generated by the devices can produce thermal strain that may cause the optical fibers and the optoelectronic devices to be misaligned.
Various passive alignment techniques have been developed, such as the use of guide pins and holes, to attempt to provide fast, easy and simultaneous alignment and attachment of an array of optical fibers to optoelectronic devices. Passive alignment typically indicates a technique for aligning a laser and an optical fiber that does not require the laser to be turned on during the alignment process; whereas an xe2x80x9cactivexe2x80x9d technique requires the laser to be turned on. However, these passive alignment techniques often do not provide a precision coupling of the optical fibers to optoelectronic devices.
Accordingly, there is a need in the art to provide a method and apparatus for precise, fast and easy alignment and attachment of optical fibers to optoelectronic devices, which may be mounted on a circuit board. In addition, there is a need in the art to provide an inexpensive method and apparatus for aligning and attaching optical fibers to optoelectronic devices so that the method and apparatus are suitable for mass production. Finally, there is a need in the art for a small apparatus coupling optical fibers to optoelectronic devices so that the apparatus can easily be mounted on a circuit board.
In view of the above-stated disadvantages of the prior art, an object of the present invention is to provide an optoelectronic mounting structure that may be used in conjunction with an optical transmitter, receiver or transceiver module.
Another object of the present invention is to provide an apparatus and process for quickly, easily and precisely aligning and connecting at least one optical fiber to at least one optoelectronic device by using highly precise machinery and adhesive.
Another object of the present invention is to provide an apparatus and process for aligning and connecting at least one optical fiber to at least one optoelectronic device while maintaining a gap between at least one optical fiber and at least one optoelectronic device.
Another object of the present invention is to provide an apparatus and process for quickly, easily and precisely aligning and connecting at least one optical fiber to a wide variety of device(s) or object(s) by using highly precise machinery and adhesive.
Another object of the present invention is to provide an inexpensive method and apparatus for aligning and connecting at least one optical fiber to at least one optoelectronic device so that the method and apparatus are suitable for mass production.
Another object of the present invention is to provide an inexpensive method and apparatus for aligning and connecting at least one optical fiber to a wide variety of device(s) or object(s) so that the method and apparatus are suitable for mass production.
Another object of the present invention is to provide a small apparatus for coupling at least one optical fiber to at least one optoelectronic device so that the apparatus can easily be mounted on a circuit board.
In accordance with the first object of the present invention, an embodiment of an optoelectronic mounting structure comprises: (1) a mounting structure; (2) an array of optoelectronic devices adapted to the mounting structure, the optoelectronic devices having at least a first end; (3) an array of optical elements, the array of optical elements having at least a first end; (4) the first end of the array of optical elements proximate to the first end of the array of optoelectronic devices in such a manner that one or more optical elements is optically aligned to one or more optoelectronic devices; and (5) a heat spreader passing along a surface of a head region of the mounting structure. The mounting structure may be a flexible printed circuit board. Thermal vias or heat pipes in the head region may transmit heat from the mounting structure to the heat spreader. The heat spreader may provide mechanical rigidity or stiffness to the heat region. In another embodiment, an electrical contact and ground plane may pass along a surface of the head region so as to provide an electrical contact path to the optoelectronic devices and limit electromagnetic interference. In yet another embodiment, a window may be formed in the head region of the mounting structure so as to provide access to the heat spreader. Optoelectronic devices may be adapted to the heat spreader in such a manner that the devices are accessible through the window in the mounting structure.
In accordance with other aspects of the present invention, an optical transmitter, receiver or transceiver module is provided that includes a flexible printed circuit board that is bent at an angle, forming a head region, buckle region and main body region. The flexible printed circuit board supports the electrical components and circuitry of the present invention.
An array of optoelectronic devices, a driver or amplifier chip, a photo-detector, conducting lines, and electronic components may be mounted on a first surface of the head region of the flexible printed circuit board. The optoelectronic devices send and or receive light to and from optical fibers. The optoelectronic devices may be mounted on top of a spacer that may be attached to the head region of the flexible printed circuit board. The spacer raises the height of the optoelectronic devices so that they may efficiently communicate with the optical fibers and other electrical components that are mounted on the head region of the flexible printed circuit board. Alternatively, the optoelectronic devices may be mounted on an optoelectronic mounting structure that is accessible through a window in the flexible printed circuit board. When the optoelectronic devices function as emitters for emitting optical signals into optical fibers, they may be oxide-confined vertical cavity surface emitting lasers; if the optoelectronic devices function as receivers for receiving optical signals from optical fibers, they may be photo-detectors formed on a semiconductor chip. The driver or amplifier chip modulates and drives the optoelectronic devices. An optical power control system may monitor, regulate and stabilize the temperature, power and wavelength of the optoelectronic devices. Additionally, an attenuator may improve the performance of the optoelectronic devices by attenuating the optical energy emitted from the devices. Similarly, a conditioner may improve the performance of the optical fibers by conditioning the launch of the optical energy into the fibers.
The remaining electrical components and circuitry of the optical module may be located on the main body region of the flexible printed circuit board.
The buckle region of the flexible printed circuit board, the region connecting the main body region and head region, absorbs any stress that may occur in connecting a fiber optic cable to the present invention and assists in providing alignment between the optical fibers and optoelectronic devices.
A first ferrule, packaging an array of optical fibers, is mounted on top of the array of optoelectronic devices on the first surface of the head region of the flexible printed circuit board. Highly precise machinery optically aligns aligns the array of optical fiber in the first ferrule to the array of optoelectronic devices. A gap or interstitial space is established between a second end of the first ferrule and a top surface of the optoelectronic devices. Optical adhesive is dispensed in the space or gap between the first ferrule and the optoelectronic devices so as to maintain the precise axial alignment of the array of optical fibers to the array of optoelectronic devices. The optical adhesive provides a optically transparent and stable medium between the optoelectronic devices and the fibers.
After the optical adhesive is cured, a dam may be formed on the first surface of the head region of the flexible printed circuit board. A second adhesive is dispensed inside the dam, and the second adhesive further mechanically stabilizes the first ferrule to the flexible printed circuit board. The second adhesive also protects the circuitry in the immediate vicinity of the optical fibers and optoelectronic devices. For airtight sealing of the optical module, the surface area of the second adhesive may be covered with a third layer, such as a gel silicon resin.
After the first ferrule is firmly attached to the head region of the flexible printed circuit board, the circuit board is wrapped around and attached to a circuit board mounting structure with an adhesive.
A housing snaps or otherwise mounts with screws, adhesives or other means onto a first end of the circuit board mounting structure, enclosing the head region of the flexible printed circuit board along with the first ferrule that is mounted on the head region. The first ferrule fits inside a longitudinal cavity extending from a first end of the housing to a second end of the housing. Ridges inside the longitudinal cavity grab and hold the first ferrule in place.
In operation, a fiber optic cable from an external system is brought in proximity to the housing to create an optical connection. A second ferrule is located at one end of the fiber optic cable, and the second ferrule is designed to mate with the second end of the housing. The second ferrule is inserted into the second end of the housing and ridges in the housing""s longitudinal cavity engage and hold the second ferrule in place. Once inside the longitudinal cavity, the second ferrule mates with the first ferrule by engaging guide pins located on a front end of the first ferrule with guide holes located on a front end of the second ferrule. As a result, the array of optical fibers packaged in the two ferrules are axially aligned. Upon mating the ferrules together, light may be transmitted from the fiber optic cable through the two ferrules and to the optoelectronic devices that are adapted to the flexible printed circuit board. The optoelectronic devices convert the light into electrical signals for processing and vice versa.
A further significant aspect of the present invention involves a process by which the first ferrule is aligned and connected to the array of optoelectronic devices, according to a preferred embodiment of the invention. A process of aligning and connecting the first ferrule to the array of optoelectronic device comprises the following steps:
1. Aligning the optical fiber(s) packaged in the first ferrule with the optoelectronic device(s) so that each optical fiber is optically aligned to a corresponding optoelectronic device(s);
2. Depositing optical adhesive on a top surface of the optoelectronic device(s);
3. Placing the first ferrule on top of the optical adhesive while maintaining the alignment of step 1;
4. Tacking and curing the optical adhesive; and
5. Forming a dam around the first ferrule that is mounted on the head region of the flexible printed circuit board, dispensing adhesive and curing the adhesive.
Although the above-stated process has been discussed in terms of accurately aligning and attaching the first ferrule to the array of optoelectronic devices, the same process may be used to accurately align and attach a single optical fiber or an array of optical fibers to a single optoelectronic devices or an array of optoelectronic devices. Similarly, the process may be used to accurately align and connect at least one optical element to a wide variety of devices and objects other than optoelectronic devices. The optical element may comprise a lenslet array, diffractive optic array or an optical fiber. For example, the process may be used to connect an optical element to a micro-electromechanical system (xe2x80x9cMEMSxe2x80x9d) or a biological or chemical sample held on a substrate.